1. Field of the Invention
The present invention relates to ink jet printing machines and, more particularly, to improvements in the liquid level control (LLC) plate within the ink reservoir of the printhead of such machines, which plate has an undersurface or ink side which engages the aqueous liquid jet ink and controls the level of the ink within the reservoir. The LLC plate also has an upper surface, or paper side, and a jet passage having a rim, or lips, through which the aqueous ink is passed, in controlled spurts, against a copy paper to form images thereon.
2. Prior Art
Conventional LLC plates are formed of a base metal of iron-nickel alloy and the lips are formed of high phosphorous nickel metal in a thickness of 3 microns. A protective layer of low phosphorous nickel is then applied thereover to provide a corrosion barrier to the aqueous jet ink. A top layer of Parylene C, a soft polymer material, is applied over both sides of the LLC plate, including the lips, as a hydrophobic coating. Finally chromium metal is sputtered over the ink side of the LLC plate to render the undersurface or ink side less hydrophobic and more wetable by the aqueous ink to avoid the formation of bubbles. Thus, as required for ink maintainability, the external surface or paper side of the LLC plate is ink-repellant, and the undersurface or ink side is ink-attractive.
A corrosion problem exists with the high phosphorous nickel lip material due to the high incompatibility of such material with aqueous jet inks which, when in direct contact therewith, dissolve the lip material. The protective coating of low phosphorous nickel does not provide adequate protection against such dissolving action but the Parylene C does provide an adequate barrier. However, the Parylene C coating is relatively soft and subject to removal by contact during handling or mechanical abrasion, thereby exposing the phosphorous nickel lip coatings to contact with the aqueous jet ink during operation of the printer, resulting in lip corrosion and reduced print quality.
The present invention resides in the discovery of an entirely metallic LLC plate for aqueous ink jet printing machines, such as of the acoustic and thermal types, which is non-corrosive by aqueous jet inks and is resistant to damage by contact during handling or mechanical abrasion. The present LLC plates are formed of a corrosion-resistant base metal such as iron-nickel alloy but the lips are formed of gold and the upper surface or paper side, including the gold lips, is overcoated with a hydrophobic gold encapsulation which is corrosion resistant. The undersurface of the LLC plate is coated with sputtered chromium. The upper surface of the gold preferably is reacted with an organic thiol self-assembled monolayer (SAM) or mercaptan compound, most preferably a cross-linked SAM, to further increase its hydrophobic properties.